Technical Field
The present disclosure relates to a drill ship, and more particularly, to a ventilating apparatus for a drill ship, which allows the drill ship sailing around an arctic region to maintain appropriate temperature and pressure.
Description of the Related Art
Due to the rapid international industrialization and industrial development, the use of the earth's resources, such as oil, is gradually increasing. Accordingly, stable production and supply of oil is emerging as a very important worldwide issue.
For this reason, much attention has recently been paid to development of small marginal fields or deep-sea oil fields, which have been ignored because of their low economic feasibility. Therefore, with the development of offshore drilling techniques, drill ships equipped with drilling equipment suitable for development of such oil fields have been developed.
In conventional offshore drilling, rig ships or fixed type platforms have been mainly used, which can be moved only by tugboats and are anchored at a position on the sea using a mooring gear to conduct an oil drilling operation. In recent years, however, so-called drill ships have been developed and used for offshore drilling. The drill ships are provided with advanced drilling equipments and have structures similar to typical ships such that they can make a voyage using their own power.
Meanwhile, a moonpool is formed at the center of a drill ship equipped with a variety of drilling equipments, such that a riser or a drill pipe for drilling oil or gas existing under the sea bed is vertically movable through the moonpool.
FIG. 1 is a side view illustrating a conventional drill ship which performs a drilling operation on the sea.
A derrick 2 is fixedly installed on a deck of a drill ship 1. The derrick 2 is a large complicated structure provided with beams and a variety of drilling equipment. The derrick 2 is a type of tower in which all drilling equipment installed around the moonpool 3 of the drill ship 1 are integrated. In addition, the derrick 2 is provided for vertically moving drilling equipment such as a drill pipe 5. The derrick 2 vertically moves the drilling equipment to a desired position by winding or unwinding a wire rope coupled to the drilling equipment by a winch operation. The drill ship 1 may use one derrick or two derricks.
A worker drills for submarine resources stored in an oil well 13, which is located in a reservoir 12 under a sea bed 6, by moving a riser 4 and a drill pipe 5 downwardly through the moonpool 3 formed at the center of the drill ship 1.
The riser 4 is a member that moves to the sea bed 6 before the drill pipe 5 moves downwardly to the oil well 13, and it provides a passage through which mud is returned. When the riser 4 is installed, the drill pipe 5 moves downwardly through a sea bed layer 11 to the oil well 13 along the inside of the riser 4.
In the case where the riser 4 moves downwardly to the sea bed 6 or the drill pipe 5 moves downwardly to the oil well 13, short risers 4 or short drill pipes 5 are coupled together and move downwardly. A blowout preventer (BOP) 7 is installed on the sea bed 6 to prevent abnormal pressure from blowing out along the drill pipe 5. A casing 8 is fixed to the sea bed layer 11 by cement, and the drill pipe 5 with a drill bit 10 is inserted into the casing 8. Then, the submarine resources are drilled. The drill bit 10 may be overheated by heat generated when the drill bit 10 drills the ground. Therefore, a mud 9 is inserted into the drill pipe 5 in order to prevent the overheating of the drill bit 10, and the mud 9 serves to lubricate the drill bit 5, thereby further facilitating the drilling operation. The mud 9 is discharged out of the drill bit 10 and is returned through the casing 8 and the riser 4. When the drilling operation is completed, the drill pipe 5 is carried to a drill floor through the moonpool 3 and then is separated and delivered to a storage facility.
In the case of the conventional drill ship, as described above, the derrick has an opened structure in which steel pipes are coupled together, like a power transmission tower installed on the ground. Therefore, natural ventilation is possible without any separate mechanical ventilating apparatus.
However, if the conventional derrick having the opened structure is installed in a drill ship which sails around an arctic region, a variety of drilling equipment is exposed to at below zero temperatures for a long time. Consequently, the drilling equipment may not operate normally.